1. Field of the Invention
Aspects of the present invention generally relate to devices and methods for radio frequency detection in semiconductor processing. Further embodiments relate to devices and methods for detecting low level microwave excursions during UV curing of substrates and wafers.
2. Description of the Related Art
Silicon containing materials such as silicon oxide, silicon carbide and carbon doped silicon oxide films are frequently used in the fabrication of semiconductor devices. Silicon-containing films can be deposited on a semiconductor substrate through various deposition processes, such as chemical vapor deposition (CVD). For example, a semiconductor substrate may be positioned within a CVD chamber, and a silicon containing compound may be supplied along with an oxygen source to react and deposit a silicon oxide film on the substrate. In other examples, organosilicon sources may be used to deposit a Si—C bond. Film layers made by CVD processes may also be stacked to form composite films. In some processes, ultraviolet (UV) radiation can be used to cure, densify and/or relieve internal stresses of films or film layers created by the deposition process. Additionally, byproducts such as water, organic fragments or undesired bonds may be reduced or eliminated. The use of UV radiation for curing and densifying CVD films can also reduce the overall thermal budget of an individual wafer and speed up the fabrication process.
A number of various UV curing systems have been developed which can be used to effectively cure films deposited on substrates. U.S. Pat. Nos. 6,566,278, 6,614,181, 7,777,198 and 8,203,126 (assigned to Applied Materials, Inc.) describe using UV light to treat deposited films, and are incorporated by reference herein in their entirety.
UV light may be produced by microwave generators or radio frequency (RF) energy sources exciting gases within UV bulbs. Radiofrequency (RF) and microwave (MW) radiation may be considered electromagnetic radiation in the frequency ranges 3 kilohertz (kHz)-300 Megahertz (MHz), and 300 MHz-300 gigahertz (GHz), respectively. However, the terminology RF can also be used to refer to broader frequency ranges, which include microwaves. In the context of this patent, the term RF is used in its broadest sense to include microwaves.
In order to provide high intensity UV in the curing process, a high voltage power supply and a lamphead with an electrode-less bulb can be used. For example, a power supply can provide voltage to magnetrons embedded inside of a lamphead. The magnetrons generate the microwave that in turn ignites the gases in the bulb to generate the UV used for processing the wafers. A fine mesh screen is positioned on the lamphead that allows UV light to pass through on its way to the substrate, but that blocks microwaves. Screens may be made from stainless steel and clamped between two pieces of metal with RF gasketing to prevent microwave leakage. In case of an equipment failure, Microwave detection may be used to protect personnel from harmful doses of microwaves.
It has been discovered that low level leakage of microwaves that are safe for humans (for example 5 mW/cm2 and below) may still cause wafer damage or non-uniformities and may have detrimental effects on the properties of films that are deposited on substrates such as wafers. Damaged wafers can have shifts in uniformity and stress. For example, a small tear in the fine mesh screen allows low-level microwave leakage that is safe for humans, but that causes shifts in device uniformity and film stress. These issues are not detected until after a production run is complete, because current UV processing equipment has no means of detecting low-level microwave excursions that damage semiconductor devices on the wafers. Therefore, a need exists for devices and methods to detect and/or prevent RF and microwave leakage at levels that may damage semiconductor devices.